1. Field of the Invention
The present invention relates to image-receiving sheets for (i) thermal transfer recording such as thermal sublimation or thermal fusion transfer recording by use of thermal recording apparatus or devices including thermal printers and (ii) photosensitive, pressuresensitive transfer recording by use of microcapsules of the photo-setting type (type hardenable by light irradiation).
2. Description of the Prior Art
In recent years there have been energetically developed techniques of thermal fusion transfer recording to form transferred images on sheets of plain paper by using thermal printers, thermal facsimiles, or the like. This thermal transfer recording has been in extensive use recently in that recorders for this purpose, because of their simple mechanism, offer the advantages of easy maintenance, low prices, and low maintenance costs, that distinct and durable images can be recorded, and that color recording is possible relatively easily by using multicolor ink sheets.
Highly precise, color thermal transfer recording good in gradation reproducibility has been demanded particularly for applications to CAD/CAM systems, color copying machines, video printers, etc. Diversified improvements have been made of the recorders in thermal heads, of the thermal transfer films in the raw material, properties, layer constitution, etc. of heat fusible inks, and of the recording methods.
Image-receiving, transfer recording paper has also been improved in smoothness, oil absorbency, air permeability, etc.
For example, known techniques about imagereceiving transfer recording paper includes the following: Japanese Patent Application Kokai No. Sho. 60-255487 discloses that image-receiving paper exhibiting good gradation characteristics can be obtained by coating base paper with a heat fusible substance having a higher melting point than that of the heat fusible ink on the transfer film used.
Japanese Patent Application Kokai No. Sho. 57-182487 discloses that image-receiving sheets capable of recording steadily distinct images free of density unevenness can be obtained by providing sheets with image-receiving layers containing an oil-absorbing pigment which has an oil absorbency of at least 30 ml/ 100 g (measured in accordance with JIS K5101)
The thermal sublimation transfer recording technique using a thermal recording device such as a thermal printer comprises opposing an image-receiving sheet to a sublimation type of thermal transfer film prepared by applying a readily sublimable dye on a substrate such as paper or film, and transferring an image onto the image-receiving sheet from the transfer film by heating it with a thermal head or the like.
According to this technique, full-colored hard copies of high gradation quality can be obtained from readily sublimable dyes of yellow, magenta, cyan, and if necessary, black in color by heating them successively to transfer images.
As regards the prior art of thermal sublimation transfer recording, examples of known techniques include the following: Japanese Patent Application Kokai No. Sho. 57-107885 discloses a thermal recording sheet (image-receiving sheet) having on a substrate a coating layer containing a saturated polyester.
Japanese Patent Application Kokai No. Sho. 61-270192 discloses an image-receiving, thermal transfer recording sheet which has a microporous layer of thermoplastic resin or synthetic rubber between a substrate and an image-receiving layer. The thermoplastic resin is exemplified by a saturated polyester, polyurethane, vinyl chloride-vinyl acetate copolymer, and cellulose acetate propionate and the synthetic rubber is exemplified by styrene-butadiene rubber, isoprene rubber, and urethane rubbr. The micropores of the intermediate layer are formed by using a blowing agent or the like.
Japanese Patent Application Kokai No. Sho. 62-151393 discloses an image-receiving, thermal transfer recording sheet which has an elastomer layer between a supporting sheet and a dye-receicing layer. The elastomer is exemplified by butadiene rubber, isoprene rubber, nitrile rubber, styrene-butadiene rubber, chloroprene rubber, urethane rubber, silicone rubber, acrylic rubber, and natural rubber.
On the other hand, the photosensitive, pressure-sensitive transfer recording method using microcapsules of the photo-setting type is as follows: The recording system of this method comprises a transfer sheet having a support coated with microcapsules and an image-receiving sheet represented by plain paper. At least one of the shell and the inner phase that construct the microcapsule is made up of a substance which undergoes a change in properties when exposed to light, heat, or both light and heat. A latent image according to a pattern of such energy is formed on the transfer sheet by utilizing the above characteristic. The inner phase of the microcapsule contains a colorant which corresponds to an oil ink. The transfer sheet bearing the latent image is then combined with the image-receiving sheet, and subjected to pressure, heat, or both pressure and heat. Thereby the microcapsules (uncured) at the latent image areas are ruptured and the inner phase, i.e. the ink is transferred from the ruptured capsules to the image-receiving sheet, thus recording an image.
For example, Japanese Patent Application Kokai No. Sho. 62-39844 discloses a photosensitive, pressure-sensitive recording system for transferring images onto sheets of plain paper, the system comprising the exposure of microcapsules on a transfer sheet which enclose a photopolymerizable compound and a color dye or pigment to a pattern of light to form a latent image, that is, polymerizing the photopolymerizable compound at the exposed areas to harden the corresponding microcapsules, then combining the transfer sheet with a sheet of plain paper, and rupturing the unhardened microcapsules by applying pressure, to transfer the released colorant onto the plain paper sheet, thereby forming an image.
Japanese Patent Application Kokai No. Sho. 62-39845 discloses a photosensitive thermal transfer recording system which comprises combining a sheet of plain paper with a transfer sheet coated with microcapsules which are constructed of (i) shells made of a heat fusible substance and (ii) inner phases made of a color dye or pigment dissolved or dispersed in a photo-setting resin or in both a photo-setting resin and an organic solvent, and applying pressure and heat to the transfer sheet, thereby forming an image on the sheet of plain paper.
The above stated prior art involves various problems, examples of which are as follows:
As regards the thermal fusion transfer recording; a problem of the method of using image-receiving sheets having coats of heat fusible substance is that transferred images are lacking in long-term storage stability and particularly in heat stability; in the case of image-receiving sheets which have image-receiving layers containing an oil-absorbing pigment, the performance of transfer film depends on the melt viscosity of the heat fusible ink and on the oil absorbency of the pigment in the ink and there is still room for improvement in these properties for the purpose of providing highly precise transferred images.
As regards the thermal sublimation transfer recording; in the method of using an image-receiving sheet whick has on a substrate a monolayer coat containing a saturated polyester, the transferred image is lacking in preciseness or minuteness; further, in the method of using an image-receiving sheet which has an elastomer layer between a supporting sheet and a dye-receiving layer there is room for improving the transferred image in gradation reproducibility and in precision or minuteness.
In photosensitive, pressure-sensitive transfer recording, on the other hand, plain paper has so far been used for image-receiving sheets. However, images formed on sheets of plain paper are insufficient in qualities such as density (optical density), chroma, and resolution. In particular, multicolor transfer recording can provide no high-quality image since this recording is generally practiced by the method of transferring inks of different colors such as cyan, magenta, yellow with them combined together by superposing or overlaping.